My intercom was quite scratchy and broken when I did my COPA for Kids flight. We could communicate, and the radio transmisions and reception were fine, so I did the flight, but decided I wouldn’t fly any more kids until I found and fixed the problem. I took the aircraft back to the hangar, and started troubleshooting. I found some very puzzling symptoms.

From the pilot’s seat, if I spoke into the mic, the audio in my headset was very scratchy and broken. I tried the rear seat headset, and it was fine. I tried speaking into the rear mic while listening in the front headset, and it was fine. I tried speaking into the front mic which listening in the rear headset, and it was also fine. I then switched the two headsets between front and rear seats, and got exactly the same symptoms as before - i.e. the problem did not follow the headset, so I knew the headset was OK.

Completely baffled, I stopped for lunch. I discussed the issue with a couple of bright guys, and the best advice I got was it could be a panel jack grounded at the panel. Good idea.

After lunch, I checked out the panel jacks, but they seemed to be well isolated from the panel. I repeated the same tests I did before lunch, to confirm the symptoms were well understood, and I got exactly the same results. But, this time I noted that the problem only occured when the mic was very close to my lips. If I pulled the mic a bit back from my lips the audio was clean. I recalled that I had turned the front seat intercom volume up to max, as my passenger was very soft spoken. I turned the volume back to its usual position, and the problem went away. It seems that the intercom puts out enough audio signal to overpower the headset, if the intercom volume is at Max - only in the front seat. There must be enough loss in the longer wires going to the rear seat headset to avoid the issue.

I was very glad there wasn’t really a problem, but a bit frustrated that it took so long to come to that conclusion.